This invention relates to magnetic trackers for tracking the orientation and position of a helmet used by vehicle operators in such vehicles as tanks, planes, etc. Trackers are well known in the present area of technology and the operation of a tracker is described in references U.S. Pat. No. 4,287,809, U.S. Pat. No. 4,945,305, and U.S. Pat. No. 3,868,565.
FIG. 1 shows a block diagram of a tracker. A receiver 12 is mounted on a helmet 13. The receiver 12 is what receives the electromagnetic information of the magnetic field in the operator area. The receiver 12 is typically attached to the operator""s helmet 13 so as the helmet 13 moves, the receiver 12 will receive the information required to determine the helmet 13 position and orientation. An example of a receiver 12 would be three inductive coils which is well known in this area of technology. Three coils, one coil each to represent one axis of the triad axes in the helmet coordinate frame, exist to sense the electromagnetic field vectors to be transmitted by a transmitter 11.
Once the components of the magnetic field are obtained, it is necessary to perform calculations on the data. As a result, the data is sent from the receiver 12 to pre-amplifiers 22, 23, 24 via cable 21. The reason for three preamplifiers 22, 23, 24 is to accommodate for the x, y, and z signals of the helmet movements and to amplify the signals for processing. The output of the pre-amplifiers 22, 23, 24 are sent to a multiplexer 25 to combine the three signals. The output of the multiplexer 25 is sent to a central processing unit (CPU) 32. The CPU 32 performs calculations on the data to obtain and accurate mapping of the operator area. Filters, such as bandpass filters, can be used at any point of the system to filter out unwanted signals. Amplifiers, such as a variable gain amplifier, can also be used at any stage of the system to amplify the signals. Furthermore, it is well known that A/D converters are also required for the CPU 32 to process the data. The figure has been simplified only to show the essence of the operation and structure of currently existing trackers.
A selector switch 47 is used to control the transmission of signals to the transmitter 11 by selecting which signal will be sent. The signals are sent through amplifiers 60, 61, and 62 so that the signals have sufficient power for energizing the transmitter 11. The transmitter 11 transmits a magnetic field in the operator area back to the helmet 13. Orientation and position information is sent back to the vehicle systems via an interface so that the vehicle operates accordingly with the information. One such example would be to control the instrumentation of an aircraft.
A driver is used to supply energy to the transmitter 11 to a desired level. As is presently known, inductive coils have been used in a transmitter. A typical drive system uses three or six inductive coils driven sequentially at a fixed repetition rate. During each drive period of each coil, the coil is driven for several periods at the excitation frequency. The large coil excitation levels required are generated by placing a capacitor in series with each transmitter coil so that a high-Q series-resonant network is obtained at the excitation frequency. This resonant network is driven by a sine voltage from a drive amplifier. A high accuracy current sensing resistor provides feedback so that the coil current is driven to the desired level. In previous designs, a separate amplifier and current sensing resistor were used with each coil network. When a sine drive is applied to a network, several excitation cycles elapse before the current stabilizes, as the stored energy increases in the resonant network. It would be desirable to have a driver that does not require several excitation cycles to elapse. Further, it would be desirable to have a non-complex driver with a quicker response.
A helmet tracker including a transmitter to transmit information regarding the orientation and position of the helmet, a receiver for receiving the information, and a processor for processing the information to determine the position and orientation of the helmet. An apparatus is connected to the transmitter to attain a faster response time for the transmitter to transmit the information.